Immunoglobulins of the IgG class are attractive as therapeutic agents. IgGs exists as four subclasses in humans, IgG1, IgG2, IgG3, and IgG4. The heavy chain constant (CH) region of IgG comprises three domains, CH1, CH2, CH3, where CH1 and CH2 are linked by a hinge. Although the role of each subclass appears to vary between species, it is known that the heavy chain constant domain is responsible for various biological effector functions. The human IgG subclasses mediate a plethora of cellular immune responses through their interaction with Fcγ receptors (FcγRs), such as cell killing, complement activation, phagocytosis and opsonization. In an attempt to understand and manipulate the effects of IgG subclass binding to FcγRs, researchers have made various mutations to the constant domains of IgGs and studied the resulting IgG/FcγR interaction (see e.g. Canfield and Morrison J Exp Med 73, 1483-1491 (1991); Chappel, M. S., et al. JBC 268(33), 25124-31 (1993); and Armour, K. L., et al. Eur J Immunol 29, 2613-24 (1999)).
Fc dependent cytotoxic activity of human IgG antibodies requires binding of the Fc region of the antibody (which consists of at least a functional CH2 and CH3 domain) to an FcγR on the surface of an effector cell, such as a natural killer cell, an activated macrophage or the like. Complement-mediated lysis can also be triggered by the interaction of the Fc region with various complement components. With regard to FcγR binding, it has been suggested that several amino acid residues in the hinge region and in the CH2 domain of the antibody are important (see Sarmay, G, et al. Mol Immunol 29, 633-9 (1992); Greenwood, J et al., Eur. J. Immunol, 23(5), 1098 (1993), Morgan, A. et al, Immunology, 86, 319 (1995), Stevenson, G T, Chemical Immunology, 65, 57-72 (1997)). Glycosylation of a site (N297) in the CH2 domain and variations in the composition of its carbohydrates also strongly affect the IgG/FcγR interaction (Stevenson, G T, Chemical Immunology, 65, 57-72 (1997); Sibéril et al Immunol Ltrs 106, 111-118 (2006)).
For certain antibody therapies, it may be advantageous to engineer the Fc receptor binding properties so as to activate all, some, or none of the available effector mechanisms, without affecting the antibody's pharmacokinetic properties. The desired combination of therapeutic properties may not be available in the natural antibody repertoire. The design of antibodies with reduced effector function should be efficacious for example when the therapeutic objective is not to kill a target cell, but to block or activate a cell surface molecule on its surface without triggering cytotoxicity. Another setting in which reduced binding to Fc receptors could be desirable is when the antibody is bispecific, and its desired therapeutic properties arise from the different binding specificities. For example, a common usage of bispecific antibodies is to combine a tumor targeting specificity with a T cell activating specificity in order to trigger tumor-specific T cell killing. In this case, if the Fc portion binds to an Fc receptor, then potentially that could trigger undesirable killing of cells bearing Fc receptors by T cells, or killing of T cells by Fc receptor-bearing cells such as natural killer cells or macrophages.
Thus, there exists a need for improved biological therapies, such as antibodies with desirable properties for use in such therapies. Applicants have discovered that recombinant proteins containing substituted or otherwise modified antibody heavy chains, including recombinant antibodies and recombinant receptor-Fc fusion proteins, have altered Fc receptor binding activity, which reduce the risk of unwanted side effects, and thus provide improved therapeutic effect.